Thermally stable perfluoroalkylene ether bibenzoxazole polymers

ABSTRACT

Perfluoroaklylene ether bibenzoxazole polymers, thermally stable at elevated temperatures, are prepared by the condensation of a perfluoroalkylene ether bisaminophenol and a perfluoroalkylene ether diimidate. Because of the high thermal stability and low glass transition temperatures of the polymers, they are eminently suitable for use in aerospace applications where a wide range of temperature conditions is encountered. In particular, the polymers are useful as sealants and seals.

United States Patent Evers Nov. 5, 1974 I5 THERMALLY STABLE 3,306,876 2/l967 Kantor et 61 260/47 3,391,118 7/1968 Cook 260/61 PERFLUOROALKYLENE ETHER BIBENZOXAZOLE POLYMERS [75] Inventor: Robert C. Evers, Dayton, Ohio [73] Assignee: The United States of America as represented by the Secretary of the Air Force, Washington, DC.

[22] Filed: Sept. 26, 1973 [21] Appl. No.: 401,000

[52] US. Cl. 260/61, 260/47 R [51] Int. Cl C08g 23/00 [58] Field of Search 260/47 R, 61

[56] References Cited UNITED STATES PATENTS 3,230,196 H1966 Moyer 260/47 Primary ExaminerMelvin Goldstein Attorney, Agent, or FirmHarry A. Herbert, Jr.; Cedric H. Kuhn [57] ABSTRACT Perfluoroaklylene ether bibenzoxazole polymers, thermally stable at elevated temperatures, are prepared by the condensation of a perfluoroalkylene ether bisaminophenol and a perfluoroalkylene ether diimidate. Because of the high thermal stability and low glass transition temperatures of the polymers, they are eminently suitable for use in aerospace applications where a wide range of temperature conditions is encounteredwln: particular, the polymers are useful as sealants and seals.

11 Claims, No Drawings THERMALLY STABLE PERFLUOROALKYLENE ETHER BIBENZOXAZOLE POLYMERS FIELD OF THE INVENTION This invention relates to thermally stable fluorinated polymers which are viscoelastic over a broad temperature range. In one aspect the invention relates to a process for synthesizing the fluorinated polymers. In another aspect it relates to monomers that are used in synthesizing the fluorinated polymers.

BACKGROUND OF THE INVENTION There has existed for some time a need for thermally stable, elastomeric polymers for various aerospace seal and sealant applications. Furthermore, in order for a polymer to satisfy the requirements, it must retain its. elastomeric properties at sub-zero temperatures. Still further, the polymers should possess other desirable properties such as hydrolytic stability and fuel resis- 'tance. None of the prior art elastomers appears to meet these broad use temperature range requirements.

I It is an object of this invention, therefore, to provide thermally stable fluorinated polymers which are visco- Y elastic at sub-zero temperatures.

Another object of the invention is to provide a pro-' cess for synthesizing the fluorinated polymers.

A further object of the invention is to provide monomers for use in preparing the fluorinated polymers.

Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the following disclosure.

SUMMARY OF THE INVENTION In one embodiment, the present invention resides in a thermally stable polymer composition having the following structural formula:

wherein R is (C Fm, (.CF )O(CF O(CFz) or -(CF O.(CF O(CF and n is an integer equal to at least 2, preferably an integer in the range of about 8 to 100, inclusive. Alternatively, n can be defined as an integer having a value sufficient to provide a polymer having an inherent viscosity of at least 0.10, e.g., from about 0.10 to 1.0 when measured at 25C as a 0.2 weight percent solution in hexafluoroisopropanol.

In another embodiment the present invention lies in a process for preparing perfluoroalkylene ether bibenzoxazole polymers. Broadly speaking, the process comprises the step of reacting in an inert atmosphere 1,11- bis(3-amino-4-hydroxyphenyl)perfluoro-3,9-

dioxaundecane with dimethyl perfluorosebacimidate;

dimethyl perfluoro-3,6-dioxasuberimidate; or dimethyl perfluoro-3,6-dioxaundecanediimidate, the reaction being conducted in a solvent and in the presence of added glacial acetic acid. Examples of gases that can be used to provide an inert atmosphere include nitrogen, helium, and argon.

The condensation reaction involved in preparing the polymers of this invention is shown by the following 10 equation:

. Nii otCF 2 5 2 2 g OCH OH CO H 'Polymer of Formula (I) As seen from the equation, equimolar amounts of the bisaminophenol compound and the diimidate esters are utilized in the reaction. The mol ratio of glacial acetic acid to the diimidate ester is at least 2:1, e.g., 2 to 4:1.

It is usually preferred to utilize four molar equivalents of acetic acid for each mol of the diimidate ester. The acetic acid reacts with ammonia formed during the condensation reaction, converting it to ammonium acetate and thereby driving the reaction to completion.

upon the molecular weight that it is desired the polymer product to have, being longer for higher molecular weight products. Generally, the reaction time falls in the range of 7 to 14 days although shorter and longer periods can be employed.

At the end of the reaction period, the polymer is re.- covered and purified by a general procedure that is conventionally followed in solution polymerization processes. Thus, the reaction mixture is poured into a non-solvent for the polymer, e.g., into an alcohol such as methanol, thereby causing the polymer to precipitate from solution. The precipitated polymer is then separated from the liquid by any suitable meanssuch as by filtration or decantation. After washing the separated polymer with an. alcohol, it is then dissolved in a solvent such as hexafluoroisopropanol and again precipitated from solution by pouring the solution into methanol. After separation of the precipitated polymer, it is again washed with methanol and then dried under a vacuum. It is to be understood that the foregoing procedure can be repeated one or more times in order to further purify the product.

A more complete understanding of the invention can be obtained by referring to the following illustrative examples which are not intended, however, to be unduly limitative of the invention. 1,1 1-Bis(3-amino-4- (hydroxyphenyl)-perfluoro-3,9-dioxaundecane is a new compound which can be synthesized by the threestep procedure described in Example Dimethyl perfluorosebacimidate and dimethyl perfluoro-3,6- dioxasuberimidate are well known compounds which are described in the literature. A procedure for preparing dimethyl perfluoro-3,6-dioxaundecanediimidate is set forth in Example 11.

. EXAMPLE I a. 1,1 l-Bis( 4-hydroxyphenyl)perfluoro-3,9-

dioxaundecane Copper bronze (5.08 g; 0.080 g atom) was added to a solution of p-iodophenyl acetate (7.86 g; 0.30 mol) and 1,1 ldiiodoperfluoro-3,9-dioxaundecane (7.36 g; 0.10 mol) (a product of Allied Chemical Corp.) in 45 ml of N,N-dimethyl formamide. The resulting slurry was stirred under nitrogen at l l31 16C for 96 hours. After cooling the reaction mixture was added to a stirred mixture of 150 ml of ether and 200 ml of water. The copper salts and excess copper were filtered off and the ether layer was washed repeatedly with water until free from the reaction solvent. Evaporation of the ether gave a brown oil which was then refluxed for 15 minutes in ml of acetic anhydride. The excess acetic anhydride was distilled off and the residue was taken up in 50 ml of petroleum ether. This solution was treated with charcoal, filtered, and reduced in volume to a light amber oil. Distillation yielded 5.1 g of 1,1 1-bis(4- acetoxyphenyl)perfluoro-3,9-dioxaundecane (boiling point l95l98C at 0.55 mm Hg). This water-white oil was refluxed for 30 minutes in a solution of 5 ml of concentrated hydrochloric acid in 100 ml of methanol. The resultant solution was stripped to dryness to yield a pale yellow solid which was taken up in 600 ml of hexane. This solution was treated with charcoal, filtered and reduced in volume to 150 ml. The product.

recrystallized slowly to give 3.4 g (51 percent yield) of product in the form of white needles (melting point 8890C).

Analysis Calcd: C,37.72; H l.50 Found: C.37.60; H.l.93

Molecular weight (mass spectroscopy) Calcd: 668 I Found: 668

b. 1,1 l-Bis(3-nitro-4.-hydr'oxyphenyl)perfluoro-3,9- dioxaundecane l,l l-Bis(4-hydroxyphenyl)perfluoro-3,9-

dioxaundecane (13.3 g; 0.02 mol) was added at room temperature to a solution of ml of concentrated nitric acid in 150 ml of glacial acetic acid. The solution was stirred at 4347C for 3 hours with care being taken to control any initial exotherms. A color change from light yellow through red and back to light orange was noted as the reaction progressed to completion. The cooled reaction mixture was added to 500 ml ofice' water and the product was extracted with a liter of ether. The ether layer was washed repeatedly with water and finally with dilute sodium bicarbonate solution. The ether was stripped off under water aspirator pressure and the viscous residue was taken up in hot heptane. Distillation yielded 11.3 g (74 percent yield) of pale yellow product (boiling point l90 l95C at 0.25 mm Hg).

Analysis Calcd: C.33.26; H.l.07; N369 Found: C,33.0l; H.092; N,3.49

Molecular weight (mass spectroscopy) Calcd: 758 Found: 758

of hydrogen for 3 hours. The catalyst was filtered off and the water-white solution was reduced to dryness under water aspirator pressure. The white residue was powered and then slurried in 25 ml of distilled water. Careful neutralization with solid sodium bicarbonate yielded a buff-colored solid which was isolated by filtration and dried in a vacuum oven at room temperature for several hours. The product was dissolved in 180 ml of benzene, treated with charcoal and allowed to recrystallize from a reduced volume of 100 ml of solution. The off-white solid was redissolved in 1500 ml of heptane, treated with charcoal, and allowed to recrystallize from a reduced volume of 400 ml of solu-.

tion. Additional recrystallization from benzene and heptane yielded 1.7 g (60 percent yield) of slightly offwhite product (melting point 132135C).

Analysis Calcd: C,36.l2; H.l.73; N,4.0l Found: C,36.22; 11.2.06; N,3.77

Molecular weight (mass spectroscopy) Calcd: 698

- Found:

EXAMPLE ll Hexafluoroglutaryl fluoride (108 g) was added to a slurry of cesium fluoride (3.0 g) in tetraglyme (50 ml) and the mixture was stirred at 35C for one-half hour. The mixture was cooled to 0C to 10C and tetrafluoroethylene oxide was added through a vacuum manifold under a total pressure of about 400 mm Hg. Samples were withdrawn at various intervals for gas chromatographic analysis and the reaction was terminated when 119 g of tetrafluoroethylene oxide had been added.

The above reaction mixture was added to an excess of methanol and the product (240 g) was washed repeatedly with water and dried. This mixture of diesters was dissolved in trichlorotrifluoroethane and ammonia was bubbled through the solution. After several hours a voluminous white solid had precipitated. The reaction was terminated when the refluxing ammonia had brought the temperature of the reaction mixture down to about 0C. After warming to room temperature, the

under vacuum. Redistillation gave a fraction (43.5 g) boiling at 128C which was identified by infrared and nuclear magnetic resonance spectroscopy as NC(CF OCF CF OCF CN.

Perfluorro-3,o-dioxaundecanedinitrile, 5 fluoroisopropanol (5 ml) was added and the mixture NC(CF ).,OCF CF OCF CN, (42 g) was added dropwas stirred for several minutes until a clear, pale yellow wise to an excess of methanol (100 ml) containing a solution was obtained. Glacial acetic acid (0.25 g; trace of sodium methylate. An exothermic reaction en- 0.0042 mol) was added after which the reaction mixsued and the mixture was stirred at ambient temperature was stirred for. l 1 days under nitrogen at 50C. The ture overnight. The reaction mixture was poured into resultant viscous amber solution was slowly added to water and the product extracted with trichlorotri- 150 ml of Cold ethanol (-78C), thereby precipitatfluoroethane. Distillation gave a fraction (36.0 g) boill the P y The y o Washed Several tlmes ing at 9294C at 3.5 mm Hg. Gas chromatographi with cold methanol after which it was redissolved in trianalysis showed a single component of 99.4 percent puchlorotl'lfluoldethalle' The Polymer was repreolpltated rity.The product was identified by infrared and nuclear y P the solution lhto Cold methahol- Several magnetic resonance spectroscopy as dimethyl perfluor- Washlhgs Wlth methanol followed y 'y at lsooc 3,6 di d dii id r and 0.01 mm Hg gave 0.70 g (71 percent yield) of light amber, rubbery polymer. The polymer had an inherent Molecular weight (mass Spectroscopy) Calcd; 498 viscosity of 0.79 in hexafluoroisopropanol at 25C.

Found: 498

Analsis-Cal: EXAMPLEm Y 5322.. A run was conducted in which a polymer of the present invention was synthesized. In this run 5 ml of redistilled hexafluoroisopropanol was added to a mixture of EXAMPLE V dimethyl perfluoro-3,o-dioxasuberimidate (0.350 g; A series of runs was conducted in which polymers 0.001 1 mol) and 1,1 1-bis(3-amino-4-hydroxyphenyl)- were prepared that consisted essentially of the followperfluoro-3,9-dioxaundecane (0.702 g; 0.0011 mol), ing repeating units:

N N V l C (CF2)2O( CF2)5O(CF2.)2 /C-R prepared as described in Example 1. Glacial acetic acid wherein R is an indicated hereinabove. 1n the runs 1,1.- (0.25 g; 0.004 mol) was added with stirring to the rel-bis(3-amino-4-hydroxyphenyl)perfluoro-3,9- sulting clear amber solution. The polycondensation re- 40 dioxaundecane was reacted in equimolar amounts with action was allowed to proceed under a blanket of nitrodimethyl perfluorosebacimidate [R=(CF dimethyl gen at 53-57C for 8 days at which time the viscous perfluoro-3,6-dioxasuberimidate [R=(CF )O(CF amber solution was poured into 100 ml of cold metha- O(CF and dimethyl perfluoro-3,6- nol (78C). The precipitated white fibrous polymer di d dii id [R -(CF ()(CF O(CF was all d to le n h Clear supernatant qu 1n each run the reaction was carried out at above C, was decanted. The polymer was was Several times in the presence of glacial acetic acid utilizing hexa- Wlth Cold methanol l redissolved hexa' fluoroisopropanol (HFlP) as the reaction medium. The lluotolsoplopahoh and P P to y Pourlhg mol ratio of acetic acid to the amount of the monomers the solution into cold methanol. Thorough washing of used in each f the runs was 2;1 The procedure v the Product Wlth Cold methallol followed y tltylhg at 50 scribed in Example III was followed in recovering and 11nd mm of Hg yleldod Percent purifying the polymers. Reaction conditions are shown Y l of lollgh tubbtiry P The polymer had below in Table 1 while elemental analysis data and mllctem "lscoslty of as measured properties of the polymer products are listed in Table fluoroisopropanol at 25C. 1 [L a 7 7 E3122 5:332; :13815515133 TABLE I Thermogravimetric analysis of the polymer product in- Reaction Reaction Concentration, dicated that the beginning of breakdown in air ocm "512" W curred at 450C with a 10 percent weight loss at 500C. Differential scanning calorimetry revealed a glass tran- 1. (CF08 192 3 sition temperature ofl7C. 2) Z Z 2) 192 14 3. (CF2)O(CF2)2O(CF2) 192 20 EXAMPLE v 4. (CF2)4O(CF2)2Q(CF2) 264 20 Another run was conducted in which a polymer of this invention was synthesized. Thus, dimethyl perfluoro-3,6-dioxaundecanediimidate (0.498 g; 0.0010 mol) and 1,1 1-bis(3-amino-4-hydroxyphenyl)perfluoro-3,9- dioxaundecane (0.698 g; 0.0010 mol) were weighted into a 15 ml round bottom reaction flask. Hexa- "'Radical derived from diimidate ester. G. Equiv. equivalent weight of polymer repeating unit.

N N cs O(CF o c1=* 2 C-R C O Q n TABLE II wherein R is (CF (CF )O(CF O(CF or (CF O(CF O(CF and n is an integer sufficient to Run lnheremm Analys's T Tg provide an inherent viscosity from about 0.10 to 1.0 No. Viscosity, dI/g c H N c when measured at 25C as a 0.2 weight percent solution in hexafluoroisopropanol. 81% 3% 2. The thermally stable polymer of claim 1 in which R is cm 16 3. The thermally stable polymer of claim 1 in which I R is (CF )O(CF O(CF 4. The thermally stable polymer'of claim 1 in which 5. A process for preparing a thermally stable polymer I 20 which comprises reacting in an inert atmosphere 1,1 1-

'(ilg/dl at C in HFlP. "'Glass transition temperature as determined by differental scanning calorimetry.

The polymers appeared to be unaffected by contact with JP-4 jet fuel. For example, a sample of the polymer from run 4 was stirred in .lP-4 for one week at 60C without showing any signs of swelling.

The thermal stability of the polymers was evaluated by thermogravimetric analysis under both air and nitrogen atmospheres. Onset of breakdown in air occurred in the 400 to 450C range with complete weight loss at about 600C. Under a nitrogen atmosphere the onset of breakdown in most cases was not significantly higher, but a weight residue of 10 to percent remained at 900C.

The data in the foregoing examples indicate that the products of this invention are thermally stable, elastomcric polymers which have a low glass transition tem-.

pcrature. The broad use temperature range of the polymers and their fuel resistance render them useful for many aerospace applications, particularly as sealants and seals.

In view of the foregoing disclosure, various modifications of the invention can be made by those skilled in the art without departing from the spirit and scope of the invention. I

l claim:

1. A thermally stable polymer consisting essentially of repeating units having the following formula:

bis( 3-amino-4-hydroxyphenyl )perfluoro-3 ,9- dioxaundecane with a monomer selected from the group consisting of dimethyl perfluorosebacimidate, dimethyl perflu0ro-3,6-dioxasurberimidate dimethyl perfluoro-3,6-dioxaundecanediimidate, the reaction being conducted in hexafluoroisopropanol in the presence of glacial acetic acid.

6. The process according to claim 5 in which the reaction is conducted at a temperature in the range of about 45 to 58C.

7. The process according to claim 6 in which equimolar amounts of 1,1 l-bis( 3-amino-4- hydroxyphenyl)perfluorb-B,9-dioxaundecane and the monomer are reacted and the mo] ratio of glacial acetic acid to the monomer is about 4 to l.

8. The process according to claim 7. in which the monomer is dimethyl perfluorosebacimidate.

9. The process according to claim 7 in which the monomer is dimethyl perfluoro-3,6-dioxasuberimidate.

10. The process according to claim 7 in which the monomer is dimethyl perfluoro- 3,-dioxaundecanediimidate.

11. As a new composition of matter, l,ll-bis(3- amino-4-hydroxyphenyl)perfluoro-3,9-dioxaundecane.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3,846,376 Dated November 5, 1974 Inven Robert c. Evers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, cancel claim 11 Without prejudice.

Signed and sealed this 24th day of June 1.975.

(SEAL) Attest:

C. TLERSHALL DANN R II C. MASON Commissioner of Patents Arresting Qfficer and Trademarks FORM PO-IOSO (10-69) UscMM Dc waned,

w u.s. sovsnuuzm manna OFFICE: nu o-su-au, 

1. A THERMALLY STABLE POLYMER CONSISTING ESSENTIALLY OF REPEATING UNITS HAVING THE FOLLOWING FORMULA:
 2. The thermally stable polymer of claim 1 in which R is (CF2)8.
 3. The thermally stable polymer of claim 1 in which R is (CF2)O(CF2)2O(CF2).
 4. The thermally stable polymer of claim 1 in which R is (CF2)4O(CF2)2O(CF2).
 5. A process for preparing a thermally stable polymer which comprises reacting in an inert atmosphere 1,11-bis(3-amino-4-hydroxyphenyl)perfluoro-3,9-dioxaundecane with a monomer selected from the group consisting of dimethyl perfluorosebacimidate, dimethyl perfluoro-3,6-dioxasurberimidate dimethyl perfluoro-3,6-dioxaundecanediimidate, the reaction being conducted in hexafluoroisopropanol in the presence of glacial acetic acid.
 6. The process according to claim 5 in which the reaction is conducted at a temperature in the range of about 45* to 58*C.
 7. The process according to claim 6 in which equimolar amounts of 1,11-bis(3-amino-4-hydroxyphenyl)perfluoro-3,9-dioxaundecane and the monomer are reacted and the mol ratio of glacial acetic acid to the monomer is about 4 to
 1. 8. The process according to claim 7 in which the monomer is dimethyl perfluorosebacimidate.
 9. The process according to claim 7 in which the monomer is dimethyl perfluoro-3,6-dioxasuberimidate.
 10. The process according to claim 7 in which the monomer is dimethyl perfluoro-3,6-dioxaundecanediimidate.
 11. As a new composition of matter, 1,11-bis(3-amino-4-hydroxyphenyl)perfluoro-3,9-dioxaundecane. 